In the US, bone grafts are most commonly used in spinal fusion surgery and, more generally, in the fusion or arthrodesis of any skeletal joint. In addition, bone graft is generally used in trauma surgery for the treatment of fresh fractures and non-unions, which are typically identified as fractures within 6 months that have not healed properly. The bone graft materials typically bridge a gap between bone segments and may also provide a three-dimensional scaffold on which the bone can grow.
Bone graft treatment is also typically used in conjunction with fresh fractures where the bone has been shattered or where the patient is at a very high risk of developing a non-union fracture. Because many fractures are not this severe and can be treated with alternative methods of fixation, bone grafts are not frequently needed during fresh fracture treatments.
Two areas where bone grafts are used are in conjunction with joint reconstruction and joint revision. For example, the bone graft may be used to fill a void between the bone and joint implant in a joint reconstruction surgery. Joint revision is much more likely to need a bone graft because a large void may result from the removal of the original implant. Joint revisions that use bone graft material therefore usually require a relatively large quantity of the bone graft material.
There are different types of bone graft materials that may be used to assist a patient's body in bone regeneration. These bone graft materials are typically classified as either natural or synthetic materials.
Natural bone graft materials are classified in the following groups: Autograft is bone graft material that is obtained from the same individual that will receive the bone graft material. Allograft is bone graft material that is obtained from another human source, which typically is from cadavers. Xeongraft is bone graft material that is obtained from another species.
Bone grafts can also be categorized by their bone-forming properties as osteoconductive, osteoinductive or osteogenic. Osteoconductivity is the ability of a material to provide an appropriate scaffold or matrix upon which new bone tissue can form. Osteoinductivity is the ability of a material to stimulate the patient's own system to form new bone. Osteogenic material generates new bone tissue itself. Osteoblasts, which can be found in bone marrow and mesenchymal cells, are the only cells that can create new bone.
Autograft bone has historically been the standard of care because of its osteoconductive, osteoinductive and osteogenic properties. At the time of surgery, bone is taken from a donor site in the patient, often the iliac crest bone but others are used, and then is re-implanted back into the patient at the surgical site.
Autograft is often not used, because obtaining the graft generally requires a second surgical procedure with associated risks and expenses. The autograft also typically results in significant post-operative issues, most significantly pain. An additional type of autograft, concentrated cells from bodily fluids such as blood or bone marrow, is often used as well.
In addition to autograft, many other types of bone graft are used, including processed cadaver bone, i.e., allograft, in the form of demineralized bone matrix, and also so-called “living cell” or “stem cell” allograft. Additionally, constituents known to be involved in new bone formation, such as bone morphogenic proteins, typically produced by recombinant processing means, are used. Synthetic materials such as tricalcium phosphate, calcium sulphate, hydroxyapatite and others are used as well.
Summary of Bone Graft Characteristics by MaterialTypeOsteoconductiveOsteoinductiveOsteogenicAutograftYesYesYesBone morphogenicNoYes (strong)NoproteinsDemineralized boneYesMinimalNomatrixAllogeneic stem cellYesUnknownYesBone marrow aspirateNoYes (strong)YesSyntheticsYesNoNo
Bone graft substitutes also fall within the classification of bone filler materials. Examples of bone graft substitutes include collagen, polymers, such as silicone, and some acrylics, hydroxyapatite, calcium sulfate and ceramics.
Bone cement (such as polymethylmethacylate) can be used as a bone void filler to treat bone voids or defects. For example, the bone cement can be used to repair fractured bones and vertebral bodies. The bone cement can be used either in procedures that involve direct injection of the bone cement into the fractured vertebral body (i.e., vertebroplasty) or injection of the bone cement into the vertebral body after the height of the vertebral body is restored using a pressurized balloon (i.e., kyphoplasty).
One of the disadvantages of using bone cement is that, once it is injected inside the patient, the bone cement is an inorganic material and, as such, is treated as a foreign body. As such, the bone cement may not only negatively impact healing but can also lead to bone disease.
Additionally, the bone cement is typically stiffer than bone, which may increase the incidence of adjacent level fractures in the spine. Bone cement leakage may cause complications, and has been reported to occur in vertebroplasty and kyphoplasty procedures. If leakage does occur, the bone cement can cause soft tissue injury due to the high temperatures of the exothermic polymerization reaction. In addition, if the bone cement is forced into the vascular system, it can cause emboli.
Bone marrow and bone marrow aspirate concentrate are considered to have a significantly higher bioactivity than circulating blood or concentrated blood known as platelet rich plasma. These features mean that bone marrow is often viewed as being superior to platelet rich plasma for use in orthopedic applications such as spinal fusion and trauma surgery because the bone marrow contains progenitor cells and multipotent stem cells, which assist in the formation of new bone.
Bone marrow aspirate concentrate has become increasingly popular in bone growth applications, particularly spinal fusion and trauma surgery, because of its osteogenic properties. Traditionally, autograft was the gold standard grafting material in these procedures due to the presence of osteoblasts and osteogenic precursor cells, as well as its osteoconductive and osteoinductive properties.
To avoid the risks associated with autograft procurement, such as donor site infection and morbidity, bone marrow aspirate concentrate has been increasingly used because it has properties that are similar to autograft and allows surgeons and patients to avoid autograft procurement.
Muschler, U.S. Pat. Nos. 5,824,084 and 6,049,026, both disclose systems for preparing a bone graft in which a bone marrow suspension is passed through a porous, biocompatible, implantable matrix. Muschler indicates that the bone graft can be prepared intraoperatively for use in a person from which the bone graft aspirate was obtained.
Muschler, U.S. Pat. No. 6,723,131, discloses a system for preparing bone graft. A porous, biocompatible, implantable matrix is placed in a hollow column having caps at opposite ends. Bone marrow aspirate is placed in a syringe, which is attached to one of the caps, and then the syringe is used to urge the bone marrow aspirate through the porous, biocompatible, implantable matrix.